1. Field of the Invention
The invention relates to a network enabling a synchronous data transmission with random addressing within various sub-networks, and also to a method for creating a network of this kind for data transmission.
2. Description of Prior Art
There are a number of different network types for various cases of application. The requirements of reliability, certainty of transmission and real-time capability vary accordingly. Thus, for example, for transmitting package data such as e-mails or files, relatively few demands are made on the network concerning bandwidth and certainty of transmission. Contrary to this, for a transmission of control and safety relevant data, such as in motor vehicles, high demands are made on real-time capability and reliability, whilst here too a relatively low bandwidth can be tolerated. Such data, for which a deterministic, i.e. predictable transmission characteristic, is required, are designated as control data. With multimedia applications, for transmission of synchronous data, a real-time capability and also a medium to high bandwidth are required. In order to satisfy these requirements at costs that are as low as possible at the same time, networks which are optimized for the purposes are employed in each case.
Thus, for example in motor vehicles, there is usually at least one control data network that controls the chassis and motor functions, and also connects sensors and actuators to the control units. In addition, there is frequently a further control data network for the vehicle body functions such as lighting, air-conditioning and window lifters, and other functions of this kind. Another network for synchronous and simultaneous control data transmission can be found in the infotainment field for multimedia transmission. It interconnects functions such as telephone, navigation unit and audio system, and also one or more video systems with each other. For the field of safety too, there are special networks for controlling air bags and accident sensors. In many cases the networks were developed independently from each other in accordance with the needs of the functions to be controlled by them, and they have different transmission bandwidths. Each of them are used for running respectively different mechanisms for network management, data safeguarding, hand-shaking, and segmentation of data packages. Connectors between these different network worlds and network philosophies are formed by so-called gateways that must interconvert data and philosophies.
The stronger the logical connection between functions are, including those involving a plurality of these networks, and the more different the networks are, the more complex do these converters, i.e. the gateways, become. But also differences of the philosophies of the networks per se lead to problems. Thus, for example, the starting up of a system of several networks which are each implemented with different starting-up mechanisms is a highly complex operation that can be reliably controlled only with difficulty. Even a real-time capability of such systems is in no way given. When an ensuring of timing determinism on individual networks such as a Controller Area Network (CAN) is already an extremely complex operation, then this becomes near impossible throughout a plurality of networks and gateways. The delaying of a message between two subscribers on different networks depends not only upon the delays in the individual networks, but also upon the momentary prevailing load on the intermediate gateway or gateways, and upon the overall situation of messages momentarily waiting to be converted. Control and regulating means can hardly be applied. Although known priority control means reduce the total delay, they provide no determinism.
Another network in accordance with prior art is MOST (Media Oriented Systems Transport). MOST is defined by the MOST Specification Rev. 2.2; the MOST Cooperation November 2002 and the MOST Specification Framework Rev. 1.1; and the MOST Cooperation 1999 which are to be regarded a part of the present patent application.
This MOST network by itself makes possible a deterministic transmission of control data and synchronous data in addition to normal package data. However, in combination with other networks, a deterministic transmission is hardly any longer possible because, owing to the gateways, undefined delay times result.
A method for transmitting data via widely different networks is disclosed in U.S. Pat. No. 6,522,651. In this, an adaptation of certain data to a package size determined by the network is performed by means of a suitable algorithm. However, with this method also a deterministic transmission is not possible.
A purely deterministic transmission is possible with ISDN; see Peter Bocker, “ISDN—Das dienstintegrierende digitale Nachrichtennetz, Konzepte, Verfahren, Systeme,” Springer Verlag, Berlin 1987 (“ISDN—The Service Integrating Digital Information Network, Concepts, Methods, Systems,” published by Springer Verlag, Berlin, 1987). The global ISDN network consists of a multitude of interconnected sub-networks. In these, data are transmitted with synchronous timing at a given clock frequency. A plurality of networks of a low hierarchy level, having low data rates, are combined to form networks of higher hierarchy levels, having higher data rates. In this, fixed positions in the data frames of the higher hierarchy levels are assigned to the data of the networks of low hierarchy levels. ISDN networks are implemented exclusively as point-to-point connections. Thus, at the beginning of a communication, a point-to-point connection between two desired subscribers is established from a large number of possible subscribers. This connection now remains in existence for a certain time for communication. During this time the data to be transmitted are transmitted with synchronous timing along the physical and logical path defined during the establishment of the connection. During a connection the logical and physical path of the connection, and with it also the assignment of the positions of the data in the data frames normally remains existent. Because ISDN was originally conceived for telecommunication technology, in particular for transmission of speech and package data between two subscribers, it is optimized exclusively for point-to-point connections. A connection between a plurality of different subscribers (multicast), as is necessary in modern data bus systems, is not possible with ISDN. Basically ISDN enables a limited real-time transmission with a transit time of the order of a few 100 ms. However, this only applies when a connection has been already built up. If a connection first must be newly built up, then delay times within a range of seconds are probable. Now, in order to configure a real-time capable network with deterministic delay times by means of ISDN, in which random communication between any subscribers is possible, a connection would have to be built up at the beginning of a communication for all combinations of subscribers wishing to communicate with each other, and would need to have available the maximum necessary bandwidth needed for subsequent data transmission. Thus, in a bus system connecting, for example, 10 subscribers to each other with a maximum transmission rate of 10 Mbit per second, 45 point-to-point connections with a transmission rate of 10 Mbit per second would have to be kept available, even if this maximum data rate is used, for example, only once per second.